1. Field of the Invention
The present invention relates to bicycle drives, and more particularly to shaft drives therefor. Still more particularly, the present invention relates to a shaft drive for a bicycle, wherein a number of gear ratios are provided and wherein clutching is provided at gear shifting.
2. Description of the Prior Art
Conventional bicycle drives utilize a chain drive composed of a chain and sprockets to thereby transfer motion from the pedal crank to the rear wheel of the bicycle. There are a number of disadvantages associated with chain drives, including the danger of clothes being caught therein, stretching of the chain, and chain failure. Gear ratio variations have been incorporated in chain drives, such as the derailleur. Problems with such systems which can manifest including the chain jumping off its sprocket. Accordingly, alternative drive mechanisms for bicycles would be advantageous provided they do not suffer from the above noted disadvantages, nor pose new ones of their own. In the prior art there are several shaft drives which have been proposed and are of interest to consider.
One such shaft drive is described in U.S. Pat. No. 5,078,416. The pedal crank has connected thereto a driver bevel gear, and the rear hub has connected thereto a driven bevel gear. Appropriate bevel gear shafts connect the drive and driven gears, wherein a 2:1 ratio therebetween is preferred.
Another such shaft drive is described in U.S. Pat. No. 5,136,892. A drive gear is connected with the pedal crank, a drive shaft gearingly connects to the drive gear. At the other end of the drive shaft is a drive head. The drive head frictionally interfaces with a flat face connected to the rear hub. Selective movement of the drive head with respect to the center of rotation of the flat face achieves gear ratio variation for the bicycle.
Yet another such shaft drive is described in U.S. Pat. No. 5,342,075. A forward face gear is provided on a backing disc and is connected with the pedal crank, while an aft face gear is provided on another backing disc and is connected with the free wheel mechanism at the rear hub. Each face gear has a plurality concentric raised teeth sets. A pinion gear (aft and forward) is connected with each end, respectively, of a telescope pinion shaft. The aft pinion gear is positionable by a cable, while the forward pinion gear is positionable by the cyclist. Selection of which gear set is meshed with the pinion gears determines the speed ratio.
Clearly, a direct shaft drive is superior to a chain drive. Yet, the above recounted shaft drive mechanisms do not offer the reliability and ease of shifting provided by multiple speed conventional chain drives. What remains needed in the art is a shaft drive which affords easy and simple cable controlled gear shifting together with reliable and smooth clutching action as the gears are shifted.